The present invention relates to an apparatus used in semiconductor fabrication, and more particularly, to a chemical mechanical polishing pad.
During the manufacture of multilayer integrated circuits, it is desirable to effect planarization of the integrated circuit structures in the form of semiconductor wafers. This is usually accomplished by chemical mechanical polishing (CMP). FIG. 1 shows a cross-sectional view of a conventional CMP apparatus 10, which includes a rotating table 12 having a polishing pad 14 disposed thereon, and a wafer carrier 16 that holds a wafer 18. The wafer 18 is held in an inverted position against the polishing pad 14, with the side to be polished against the polishing pad. A predetermined pressure is exerted on the wafer 18 against the polishing pad 14. As shown in FIG. 2, an enlarged cross-sectional view, a slurry 19 is applied between the wafer 18 and the polishing pad 14. In operation, the polishing pad 14 and the wafer 18 rotate in relation to one another. The wafer is polished by mechanical abrasion from the polishing pad 14 and particles in the slurry 19 and by chemical action from the slurry 19 on the polishing pad 14. Apparatus for polishing semiconductor wafers are well-known in the art. Such planarization apparatus are manufactured by IPEC Planar and the SpeedFam Corporation among others.
In a typical CMP process, two polishing pads are used. The semiconductor wafer is first polished by using a hard pad on a primary rotating table. The hard pad planarizes the wafer surface by removing material on higher raised areas 21 faster than in lower areas 23. The wafer is then polished by using a soft pad and a lower downward force on a secondary rotating table. The soft pad removes any residual material or slurry residue on the wafer surface and improves the with-in-wafer uniformity of the wafer. During the CMP process, the CMP apparatus will generate, either chemically or mechanically, unwanted particles that degrade the performance of the circuits. When the wafer is transferred from the primary table to the secondary table, the slurry becomes dry and hard due to contact with the air. A cleaning step is required. The cleaning step may include scrubbing, rinsing and spin-drying. This cleaning step undesirably reduces production efficiency. Moreover, the transferring of the wafer between the primary table and the secondary table creates the potential for contamination of the clean environment necessary during wafer fabrication.